A topmast is the secondary mast situated immediately above the lower mast on a sailing vessel, functioning as an extension to hold higher sails like topsails. It is typically a separate, smaller spar attached to the upper section of the lower mast, often supporting the topgallant mast above it.

Key Details About Topmasts:
Structure: Located above the mainmast, foremast, or mizzenmast, it is usually secured at the top of the lower mast.

Purpose: The topmast extends the vertical height of the rig, allowing for more sail area and better wind capture.

Rigging: It supports yards for topsails and has its own supporting rigging, known as topmast shrouds and backstays.

Types: Examples include the fore-topmast, main-topmast, and mizzen-topmast.

History: Developed to increase sail area without needing one excessively tall, unstable mast.

It differs from the topgallant mast, which is located even higher up, perched above the topmast.